I'm finding it hard to rate these, for the price I would give them 5 stars on every department. But I'd rather rate them, referenced with the idea of what the very best cIEM could be.

The BA4f with the Ice Blue color

Short History

Before I started my journey into the cIEM world, I knew it was going to be tricky for me. My ears are very small, and there's an extreme bend in my ear canal, my ear canal basically goes straight up. After sending my impressions to Cosmic Ears headquarters in Sweden, Phil insisted that I would use the prefit option. The fit was fine, but the finished earpieces were too flush! Yes too flush, it's possible. Despite my ears being small they also stick out a bit, so the cable connector pinched my ear badly. Luckily Phil was extremely helpful, and completely remade the earpieces free of charge.

My current favorite listening setup for the BA4f:

The BA4f with the Ice Blue color

Short History

Before I started my journey into the cIEM world, I knew it was going to be tricky for me. My ears are very small, and there's an extreme bend in my ear canal, my ear canal basically goes straight up. After sending my impressions to Cosmic Ears headquarters in Sweden, Phil insisted that I would use the prefit option. The fit was fine, but the finished earpieces were too flush! Yes too flush, it's possible. Despite my ears being small they also stick out a bit, so the cable connector pinched my ear badly. Luckily Phil was extremely helpful, and completely remade the earpieces free of charge.

My current favorite listening setup for the BA4f:

Audinst hud-mx1 + JDS O2 amp

Comfort and Usage

Since these are my first cIEMs I did not know what to expect. Since there's this extreme bend in my ear canal, I've never actually had anything in my ear canal before the visit to the audiologist! Luckily the comfort is amazing, like you would expect from any cIEM. Coming from headphones such as the senn HD25-1 II and the german maestro gmp 8.35D the isolation is amazing. In contrast to closed headphones, these actually isolate beneath 1K (yes closed headphones barely isolate lower frequencies). Which make these ideal to use in the proximity of large machinery such as trains and busses (or my drumkit).

Sound

The first thing I noticed was the incredible 'realness' of the sound. The signature is far from neutral with the boosted bass. But my mackie studio monitors, and the Mackie MR8 mk2 and the BA4f are quite similar in sound.

The frequency response sounds very 'straight' not as in neutral, but as in not jagged. Most frequency responses have terrible peaks and valleys in them, but I think the realness of the sound comes from the fairly smooth frequency curve.

Now there most certainly is a boost in the bass, but it's not that much. The presence of the bass seems to come more from extension and tightness, than from a big bass boost. I do like the bass a lot, it's very 'visceral' and detailed, but has great punch. That said, the midbass is boosted too much for me, which is why I tune down the midbass with an equalizer.

The mids are indeed very real sounding, they have great clarity and seperation. However, I do feel like the (mid)bass boost takes away some clarity from the middle frequencies. Consequently, taking about 3db in the 150-250hz region does improve the overall clarity of the sound. This is to be expected of a fun signature though.

Back to the mids, I love male vocals, but higher vocals seem slightly distant in some cases. The quality of the vocals seems to be very recording dependent, just like the early review on the BA4r by Project86, the BA4f loves good recordings, good sources and will get very angry when served up with sh**ty equipment and music. The BA4f has become much less picky than the early BA4r, but it still gives you an honest representation of the music (something I love). The BA4f does seem to be aimed primarily at the bass and mids, the treble is there but it's definitely softer. Unlike something like the HD650, which is very warm sounding, the treble in the BA4f still has some sparkle and detail but as mentioned before it's a bit softer. Despite the softness, the treble has great detail, good extension, and again sounds very real!

I have recently acquired the akg K702 anniversary edition full sized open headphones, and going back the BA4f makes it painfully clear that the treble is the weakest link in the BA4f. Although it's not quite fair to compare a cIEM to a full sized open headphone, I do feel that treble extension and detail is somewhat lacking in the BA4f. This is where there is room for improvement, and I hope to see an improved treble response in the new BA5 and BA6 models.

Soundstage, imaging and soundstage is a bit harder too judge, since this is my first cIEM, and my only other uIEM is the TDK BA200. First of all, I don't feel like it's lacking anything. The only headphone where I was actually so bothered by the soundstage that I had to return it was the senn HD25-1 II. There doesn't seem to be Any stage in that headphone!

In the BA4f I feel that seperation > imaging > soundstage. The stage is fairly small but very accurate, imaging is very, very solid, and seperation is quite superb. Again, it is recording dependant, listening to Ritual Union from Little Dragon gives a sudden increase in soundstage.
I don't think I could expect much more from any < €400 cIEM. Soundstage does get bigger using better gear. When going from the DX50 to the O2 I am getting bigger stage, a stronger image, paired with a fuller sound, better clarity and slightly more 'shimmer'.

Conclusion

The BA4f seems to be an incredible bargain at its current price point of €320. It's fullness and realness make me think it comes very close to the performance of the reference UERM, although the UERM is priced quite a bit higher.
In short: the BA4f sounds very realistic and full paired with a very punchy visceral bass and slightly softer treble, but overall fantastic clarity. I'd rather have the bass boost cut off a bit earlier, it extends a bit to far towards the mids for me. But again, this is to be expected from a fun signature.

If you like your clarity above all else, I suggest the BA4r. But if you want more bass presence paired with that clarity, I do suggest the BA4f.